No I guess you are right Dénes
Since the V-3 (aka also model A) D-EBRQ is shown without canopy in the Bücker book, I suppose if you have a photo of it with a closed cockpit, then it is not THAT which makes the difference between A and B models.
When checking Lange (which I should have done in the first place
) I suppose we again have the engine as the "villain"....
Model A used a 55 hp Zündapp engine
Model B used a 60 hp Walter Mikron (40 built)
I guess the "greenhouse" then could be put on and off at pretty much the teachers own choice....
Cheers
Stig